The manufacture of polyethylene resins in a fluidized-bed gas phase process has been the subject of a great deal of development effort and expense.
One of the problems in using a fluidized-bed gas phase process to form polyethylene resins is making a resin with desirable properties, particularly properties appropriate for blow molding purposes, while still having a high productivity and avoiding production problems, e.g., sheeting and the like. Therefore, it would be desirable to obtain a resin product with desirable properties, e.g., sufficiently high Environmental Stress Crack Resistance (ESCR) and proper die swell, while also achieving high catalyst productivities, using a fluidized-bed gas phase process.
U.S. Pat. No. 5,166,279 refers to processes for the gas phase co-polymerization of ethylene, in which polyethylene resins are formed. However, the processes disclosed in that patent are said to provide products with reduced die swell, in contrast with the processes herein, which provide polyethylene resins with increased die swell. Also, the disclosed ESCR levels are low in relation to the densities of the resins. That is, the ESCR Index (described below) is below 1.0. Further still, the disclosed catalyst productivities for low reactor temperatures are low.
Processes for gas phase polymerization of ethylene are disclosed in WO 01/77191 but neither ESCR nor die swell is discussed.
Other background references include U.S. Pat. Nos. 2,825,721, 3,622,521, 3,779,712, 3,970,613, 4,011,382, 4,517,345, 4,540,755, 4,543,399, 4,564,660, 4,588,790, 4,621,952, 4,803,251, 4,933,149, 4,994,534, 5,965,675, 6,482,901, and 6,627,713; U.S. Patent Application Publication No. 2002/0042482; EP 0 562 203 A, EP 0 562 204 A, EP 0 562 205 A, EP 0 640 625 A, EP 0 870 773 A, EP 1 207 170 A, EP 1 240 212 A, and EP 1 303 546 A; WO 2001/30871, WO 2002/40556, WO 2002/42341, WO 2004/060923, and WO 2004/094489; and JP 2004-091739.